Potentiometer construction



April 26, 1960 H.M. SCHENDEL POTENTIOMETER CONSTRUCTION /NVNTOI?.Hzeaskr M. SCHENDEL.

' BY HIS ATTORNEYS. HARRIS, K/acH, Fosrcz & HARRIS United States PatentPOTENTIOMETER CONSTRUCTION .Herbert M; Schendel, Santa Ana, Califi,assignor, by mesne assignments, to Beckman Instruments, Inc., Fullerton,Calif a corporation of California Application March 11, 1957, Serial No.645,081

13 Claims. (Cl. 338-143) My invention relates to constructions forpotentiom- .-eters and the like. More specifically, it relates to arestainer or positioning device for holding or spacing. the turns of amulti-turn winding.

'A problem often encountered in the electrical arts is ,the arcuatepositioning of such turns relative to each other and relative to ahousing. A typical example is nthe positioning of a multi-turnresistive-winding in a housing to be'contacted by a movable wiper, as inthe $1311. of making multi-turn potentiometers, resistors, delay .lines,etc. "While applicable to any multi-turn environ- -ment,;the inventionwill beparticularly exemplified with referenceqto multi-turn or helicalpotentiometers.

; It; is an-[important object of the inventi-onto provide ,an improvedstructure for accurately positioning the turns of a multi-turn winding.A further object is to provide a simple and inexpensivepositioningstructure of this character comprising a tubing corrugated inthe de- ,sired pattern of the multi-turn winding. -ther objects ;,-lie-.in the-novel association of such a positioning structure with a housing;also in the constructional features of the positioning structure and themanner: or method by which it is associated withthewinding orthe housmg.

.tAccordingzto the preferred practice of: the invention,

aal'thinewalled tube is=first corrugated inthedesiredtpatr-tern.-of-;thewinding, the ,winding-beingthen positioned thereimlthe whole. being thenpositioned in .a tubular avhousing. In the potentiometer .art,- forexample,. the lmulti-turn I resistance. element .will present .aninwardly- :exposed ihelical surface along which .a. suitably. guidedrcontactrnay move. ;In this or similar environ-ments, the :inventionprovides, for. accurate placing. orspacing ar the ltiurns. .It allowsthe windingto be closer to the'housing ithangistthe CfiSBxWlthconventional. constructionsand permits theme of .thimwalledhousingsresulting in greater tcompactness. Metal housings are particularlydesirable from the standpoint of durability, shielding-compact- .DCSS,Z1Hd dissipation and equalizationof-heat. tine-addition, for anygivenoutside diameter of the po- Ltentiorneter, thewmulti-turn resistancecoil can have a ilarger diameter and thereby improve -resolution andslinearity. This-"becomes a striki-ngaadvantage in the socalledminiature size potentiometers now in demand for tmissileguidance,transistorized circuitsend other miniature or sub miniature controlsystems employing multiturn-transducers or control-devices made inaccordance :withthe invention.

"The drawing illustrates preferred embodiments'of the invention andwillsuggest variations within thelscope of the invention. Referring to thedrawing:

Fig. l isja longitudinal cross-sectional view of a miniaturefpotentiometer embodying. some .of the features of th inv n i a Fig. 2 isa transverse fragmentary view takenitlong the line 2--2 of Fig. 1;

2,934,732 Patented Apr. 26, 1960 Fig. 3. is an enlarged fragmentary viewof a single turn of .the device; and

Fig.--4 is a similar fragmentary view of an alternative .;construction.

Referring particularly to Fig. 1, the potentiometer is shown asincluding a thin-walled tubular housing 10 having a. cylindricalinterior surface 11. ,ing can ;be..made of any suitable material,distinct ad While this housvantag'es arise from the use of a metal inthose instances where, compactness, increased heat dissipation or1mproved isothermalrconditions are desired. The ends of i the housinglflare suitably closed, as by end members .12 and 13. Pins 14 exemplifymerely one way of holding the endmembers 12 and 13 in place.

Within the housing 10 is a winding-positioning ele- -ment show-nascomprising a tube 16 corrugated in a .heIic'aI'pattern. *In thisembodiment, the tube-16 is made of thinmetal, the corrugations beingproduced by external or internal pressure respectively applied while thetube. is over a male. die or in a female die. The resulting-corr-ugatedtube 16 will have an outer surface 17 procrests. are formed by thecorrugations of the tube 16.

.It is preferred that the helical crest 18 be in engagement with theinterior surface 11 of the housing 10. A suflice but supplementaryattachment means can be used. In thisrlatteninstance, an interveningadhesive can-be employedxor. the end turns of the crest can be pinned,asolderedyor'welded to thehousing -11. Alternatively or frictionalcontact in the zone of engagement will often in addition, the ends ofthe tube 16 may pressurally'engage shoulders 23 and 24 of the endmembers 12 and--13.

.A washer'25- is shown between the shoulder 24 and the lower. end of thetube 16. The thickness of this washer will determine'the'longitudinalpressure applied to the --tube 16. '.Usually:only suflicient pressure isapplied to :preventalongitudinal movement of the tube 16 but it will :beapparent that increased longitudinal pressure can be uem-ployedtorexpandthe corrugations against the cylindri- -cal interior surface-11 of thehousing 10. The invention .comprehcnds any suitable means for applyingsuch longitudinal pressure to cause minute expansion of the tube 16 toclamp it within the housing.

',.'I'l1e inWard1y facing helical trough -22 forms a multiturn w mdingreceiving trough or space facing toward the :common axis of the tube ldan'd'the housing 10. A rmultii-turn winding '30 is disposedin thistrough and will 2 be positioned orshaped thereby to conform to thepredetermined multi-turn pattern of the trough. This is a dis-;tinctly;advantagesousifeature of the present inventionbecausetaitroughlofpredetermined pattern can be formed in the.tube F16,after which a winding of normally different patterncan be inserted, theultimate pattern of the *windingaconforming'to the pattern of thetrough. By

-normallytdiiferentpatternI have reference to a devia- :tion in spacingor size of the'turns. For example,-=it'is :the usualpracticetoproduce'the winding 30 of a helical form slightly larger thanthe trough 22 so that it tends to expand therein upon release from theinitial contractionnecessaryto dispose it in the trough. .The windingcan be retained in the trough by friction or by cementing it therein.The preferred practice is to pin or weld one end of the core of thewinding relative to the tube 16 and then-exert an unwinding pressure onthe other end to'iexpand the winding before this other end is similarlyattachedto the tube 16.

, .Thewinding 30illustrated in Figs. 1,2 and-3 is-com posed of amulti-turn core 32, typically insulated copper Wire, with a resistancewire 33 wound therearound in contacting or spaced turns. The preferredpractice is to employ a cover 34 of insulation material over the windingso that this cover will hold the resistance wire in place and willelectrically insulate the wire 33 from the tube 16 if the latter isformed of metal and the resistance wire is a bare wire. The cover 34 isremoved in an inwardly-facing zone 35 of the winding 30 to present aninwardly-exposed helical surface engageable by the guided contact to bedescribed. It should be clear, however, that coreless windings 30 can beemployed or that other means can be employed for insulating theresistance Wire from the tube 16. In addition, the tube 16 need not beformed of metal and if made of insulating material the wire 35 may comeinto direct contact therewith. In this latter connection, it issometimes desirable to make the tube 16 of molded plastic material orother material of relatively high electrical resistivity.

Any suitable contact means can be employed to advance along the helicalmulti-turn winding 30 while being guided in a helical path or to advancefrom turn to turn of the winding 30 while being moved longitudinally ofthe housing 16. Figs. 1 and 2. illustrate guidance of a contact alongthe winding 30. As therein diagrammatically shown, a rotor 40 carriesstub shafts 41 and 42 respectively journalled in the end members 12 and13 to turn about the common longitudinal axis of the tube 16 and housing10. The rotor 40 provides a longitudinal groove 44 along which a slideror block 45 may freely advance. This block carries a looped contactmember 46 terminating in a contact 47 adapted to engage the zone 35 ofthe winding 30.

Means is provided to guide the block 45 from the tube 16 so that thecontact 47 follows the convolutions of the winding 31). In this respect,the block 45 is shown as including a pair of flanges 49 extendingloosely into the V-shaped space between each turn of the winding 30 andthe adjacent wall of the trough 22. As the rotor 40 .turns, the flanges49 follow this space and advance the block 45 along the groove 44.Guidance of such a block by flanges extending into a space defined byadjacent turns is disclosed in the earlier patent to Beckman No.2,454,986 and while the present invention can employ such a sytsem it ispreferred to effect guidance by a space formed in part by one turn ofthe Winding and in part by an adjacent wall of a trough of a memherwhich positions the winding, e.g. the corrugated tube 16.

Terminals connected by leads to the ends of the winding 30 may be ofconventional form, being shown diagrammatically in Fig. 1 as includingterminal tabs 52 extending through the end members 12 and 13. Thecontact 47 can be similarly connected by a conventional pigtail lead toa corresponding terminal member, not shown.

If intermediate taps are to be employed, the leads therefor may extendthrough aligned openings 53 and 54 in the tube 16 and the housing 10respectively. If, as shown, the opening 53 lies along a crest 18, a tapwire 55 can be welded to the exposed winding and extend directly to theexterior of the housing 10. In other instances, a tap lead 56 can beconnected to the winding through an opening 57 positioned remotely fromthe housing opening 54. In this instance, such a lead 56 may extendbetween an adjacent crest 18 and the housing 10 or may extendperipherally of the tube 16 to the opening 54 through a helical passage58 formed by the trough 19 and the housing 10. This latter procedure hasparticular advantages when it is desired that tap connections orterminals are to be on or at either or both of the end members 12 or 13.When tap or terminal leads extend along the helical passage 58 they areautomatically electrostatically shielded from the resistance element andfrom external fields. The helical passage 2,934,7sa p v v 58 is ofsufiicient size to receive several small leads if desired. Some of suchleads may run in opposite directions along the passage 58 and may bebrought out either at the front or rear of the potentiometer or both. Atap lead extending along the helical passage 58 and from the end member12 is indicated in Fig. 1 by the numeral 59. I

It is preferable first to insert the winding 30 in the tube 16 and thenposition the resulting unit in the housing 10. This is particularly truewhen taps are to be connected to the winding 30. However, it is alsowithin the scope of the invention to position the tube 16 in the housing10 and then introduce the winding 30 into the tube.

In the preferred practice of the invention, both the tube 16 and thehousing 10 are formed of thin metal. The resulting structure hasexcellent heat dissipation properties and enjoys the other advantagespreviously mentioned. It is within the scope of the invention to providetubular fittings 60 and 61 through one or both end members 12 and 13 toprovide for the ingress or egress of a heat-exchange fluid acting as acoolantor heat-regulating fluid. Such a fluid may freely circulatethrough the helical passage 58, being guided thereby to flow adjacentall portions of the winding 30 and in excellent heat transfer relationthereto.

It is sometimes desirable to insulate the tube 16 from the housing 10 orto further insulate the winding 30 therefrom. Fig. 4 illustrates a thinmetal corrugated tube 64 coated on both sides with layers 65 and 66 ofelectrical insulating material. The tube 64 can thus serve as anelectrostatic shield irrespective of whether the housing 10 is made ofmetal. Additionally, the resistance wire 33 can be a bare wirespace-wound on a core 32 of insulating material or around a core space,reliance being placed upon the layer 66 to electrically insulate thecorrugated tube 64 from the resistance wire.

Various changes may be made without departing from the spirit of theinvention as defined in the appended claims.

I claim as my invention:

1. A multi-turn helical potentiometer including in combination: atubular element corrugated in a multiturn helical pattern, said tubularelement having an inner surface with a multi-turn helicalwinding-receiving trough provided by the corrugations; a multi-turnresistance winding disposed in said trough and positioned thereby as amulti-turn helical winding of a pattern determined by said trough, saidhelical winding bounding a rotor space and presenting an exposed helicalzone facing the longitudinal axis of said tubular element; a rotor;means for journalling said rotor to turn in said rotor space about saidaxis; a contact turning with said rotor; and means for guiding saidcontact to advance along said exposed helical zone in contact with theresistance winding and follow the turns thereof as said rotor is turnedabout said axis.

2. A potentiometer as defined in claim 1 in which the depth of saidwinding-receiving trough is no more than about half the diameter of theindividual turn of said multi-turn resistance winding disposed thereinmeasured in a plane including said axis to expose at least about half ofsuch turn to said rotor space.

3. A potentiometer as defined in claim 1 in which each turn of saidwinding provides a V-shaped space with an adjacent surface of thetrough, and in which said means for guiding said contact includes aflnage extending loosely into said V-shaped space and mechanicallyconnected to said contact to move same therewith.

4. A potentiometer as defined in claim 1 in which said corrugationsextend less than the full length of said tubular element, leavingcylindrical non-corrugated end 5. A potentiometer as defined in claim 1in which said tubular element is a thin metal tube and in which saidmultiwturn winding comprises a multi-turn core wound with resistanceWire surrounding said core in helical turns, said wire being coated withelectrical insulation material engaging said metal tube.

6. A multi-turn helical potentiometer including in combination: ahousing having a cylindrical inner surface; a tubular element in saidhousing corrugated in a multi-turn helical pattern and providing outerand inner surfaces each having a multi-turn helical crest and a helicaltrough formed by the corrugations, the helical crest of said outersurface engaging said cylindrical inner surface of said housing, thehelical trough of such outer surface cooperating with said cylindricalinterior surface to form a helical passage, the helical trough of saidinner surface forming a multi-turn winding-receiving space formed by thecorrugations and facing toward the longitudinal axis of said housing; amulti-turn resistance winding disposed in said winding-receiving spaceand shaped thereby into a multi-turn helical winding of a patterndetermined by said corrugations, said helical winding bounding a rotorspace and presenting an exposed helical contact zone facing saidlongitudinal axis; a rotor; means for journalling said rotor to turn insaid rotor space about said axis; a contact turning with said rotor; andmeans for guiding said contact .to advance along and in contact withsaid exposed helical contact zone of the resistance winding as saidrotor is turned about said axis.

7. A potentiometer as defined in claim 6 in which said means forjournalling said rotor includes end members closing the ends of saidhousing, a shaft to which said rotor is connected, and bearing meanscarried by at least one of said end members providing a bearing meansfor said shaft.

8. A potentiometer as defined in claim 7 in which said corrugatedtubular element is disposed between said end members and has endsurfaces receiving pressure therefrom in the direction of saidlongitudinal axis, and including means for attaching one of said endmembers to said housing while applying sufiicient longitudinal force tosaid tubular member to compress it and expand laterally the helicalcrest of said outer surface thereof into pressural contact with saidcylindrical inner surface of said housing.

9. A potentiometer as defined in claim 6 including a lead connected tosaid winding and extending along said helical passage formed by thehousing and the helical trough of said outer surface of said tubularelement.

10. A potentiometer as defined in claim 9 including end members closingthe ends of said housing and cooperating therewith in providing anenclosing structure, said enclosing structure including an opening, anda. conductor traversing said opening and electrically connected to saidlead.

11. A potentiometer as defined in claim 6 in which said housing and thehelical crest of said outer surface of said tubular element provideregistering openings, and including a conductor traversing saidregistering open ings and electrically connected to said winding at a.position intermediate its ends.

12. A potentiometer as defined in claim 6 including ingress and egressmeans communicating with said helical passage at positions spaced fromeach other along the length of such passage for circulating aheat-transfer fluid along said passage between such positions.

13. A potentiometer as defined in claim 12 including an end memberclosing one end of said housing, and in which at least one of saidingress and egress means includes a tubular connection member for saidheatt-ransfer fluid, said tubular connection member being carried bysaid end member.

References Cited in the file of this patent UNITED STATES PATENTS1,228,635 Alexander June 5, 1917 1,504,483 Klopsteg Aug. 12, 19242,379,530 Lederer July 3, 1945 2,454,986 Beckman Nov. 30, 1948 2,747,061Sorber May 22, 1956 2,750,483 Voorman June 12, 1956 UNITED STATES PATENTOFFICE CERTIFICATE OF CORRECTION Patent No, 2334332 April 26,, 1960Herbert M. Schendel It is herebj certified that error appears inthe-printed specification of the above numbered patent requiringcorrection and thatthe said Letters Patent should read as correctedbelow.

Column 1 line 21 for "arcuate" read accurate column 4, line 67, for"flnage" read me flange '0 Signed and sealed this 27th day of September1960 (SEAL) Attest:

KARL H0 AXLINE Attesting Ofiicer ROBERT C. WATSON Commissioner ofPatents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.2 93 l 732 April 26 1960 Herbert Mo Schendel It is herebfi certifiedthat error appears in the-printed specification of the above numberedpatent requiring correction and that the said Letters Patent should readas corrected below.

Column 1 line 2l for "arcuate" read accurate column 4L line 67, for"oflnage" read flange Signed and sealed this 27th day of September 1960oS EAL) Attest:

KARL H AXLINE Attesting Oflicer ROBERT C. WATSON Commissioner of Patents

